The invention relates to an arrangement for cooling exhaust gas and charge air in a motor vehicle with a turbocharger and to a method of cooling exhaust gas and charge air.
According to the prior art, the power of engines is increased using turbochargers to compress the air. However, this involves heating the air, referred to hereinbelow as charge air, to temperatures of above 100° C. owing to the compression in the turbocharger. To reduce such air heating use is made of air coolers which are arranged at the front of the cooling module and serve for cooling the charge air. The charge air here flows through a heat exchanger, which is traversed by outside air and is thus cooled. This makes it possible to cool the charge air to a temperature which is about 15-50 K above the temperature of the outside air. Under part load, it is possible to cool this charge air to virtually the outside temperature, but the recirculated exhaust gas leaves the exhaust gas recirculation cooler at a temperature between 150 and 200° C. depending on the operating point. This results, particularly at high exhaust gas recirculation rates, in a relatively high mixing temperature in the intake pipe. The reason for this is that the recooling medium used for the exhaust gas cooler is the hot engine coolant, which means that it does not appear possible to cool the exhaust gas to below 100° C. even when the exhaust gas cooler has a very good degree of exchange.
DE 103 51 546 A1, which is a subsequent publication, proposes lowering the high temperature of the recirculated exhaust gas by using a further exhaust gas recirculation cooler which can be cooled with low temperature coolant or outside air and is connected downstream of the first exhaust gas cooler which is cooled with engine coolant. After mixing the exhaust gas and charge air, the temperature here cannot be sufficiently lowered as a result of the cooling of the recirculated exhaust gas stream provided by the engine oil, so that this has a disadvantageous impact on the emissions and the consumption of a diesel engine.
If an additional cooler for the exhaust gas stream is provided which is cooled with low temperature coolant or outside air, the production costs for the arrangement increase significantly.
If, after combining the exhaust gas and the charge air, the gas stream is passed over a cooler, the arrangement becomes more cost-effective, although in this variant the particles in the exhaust gas stream give rise to a pollution problem which, given the desired heat transfer capacity, is not settled.
FIG. 3 shows by way of example a prior art arrangement with direct charge air cooling and FIG. 4 shows by way of example a prior art arrangement with indirect charge air cooling.